Add informative Error Message when sparse matrix is passed to trcrdist.public._neighbors_fixed_radius

[kmayerb]

Add informative Error Message when sparse matrix is passed to trcrdist.public._neighbors_fixed_radius

supply as csrmat to trcrdist.public._neighbors_fixed_radius does not give an appropriate error message, and consumes a lot of memory.

Add error to tell user to use trcrdist.public._neighbors_sparse_fixed_radius instead